Many flavor-improving agents employed in, for example, food additives are in the form of racemic modifications and optically active compounds are scarcely used in food additives, etc.
It is known that 2-methylbutyric acid and its esters in the form of racemic modifications widely occur in natural substances, in particular, fruits. Among these racemic modifications, 2-methylbutyric acid and C.sub.1 to C.sub.5 alkyl esters thereof have been used as food flavors for imparting a fermented smell or a matured fruit note.
Although foods and drinks containing these flavors have a nice fermented smell or a feel of matured fruits to a certain extent, they are still unsatisfactory. In addition, these products leave much room for improvement in lifting up of the top note.
In recent studies, (S)-(+)-2-methylbutyric acid and its esters and (R)-(-)-2-methylbutyric acid (i.e., the optical antipode of the former compound) and its esters are analyzed by gas chromatography and the flavor of each compound has been reported [A. Monsandle et al., Dtsch. Lebensm.--Rundsch., 86, no. 12, pp. 375-379 (1990), Tetrahedron: Asymmetry, 2, no. 10, pp. 965-968 (1991) and Kontakte (Darmstadt), no. 3, pp. 38-48 (1992)], though these reports do not relate directly to the flavors of foods and drinks.
According to these reports, (S)-(+)-2-methylbutyric acid has a pleasant, sweet and fine fruit note while (R)-(-)-2-methylbutyric acid has a penetrating cheesy-sweaty note, and (S)-(+)-ethyl 2-methylbutyrate has an etheric, sweety, unspecific, pleasant apple note at extreme dilution while (R)-(-)-ethyl 2-methylbutyrate has a first medical-phenolic note and then a fruity-sweet but unspecific note.
However each of these reports merely evaluates the flavor of a single compound having no relation directly with the flavors of foods and drinks. Namely, none of them discloses the addition of (S)-(+)-2-methylbutyric acid or its esters to a food or a drink in practice followed by the evaluation of the flavor and lifting up of the top note of the food or drink.